In glaucomatous eyes, the optic nerve head (ONH) undergoes characteristic deformations, as do other associated ocular structures, such as the lamina cribrosa (LC) and the central retinal vessel (CRV). The glaucomatous visual field (VF) defects that result from ONH changes, however, don’t typically occur uniformly in the VF, but rather tend to form first as a localized scotoma.
Researchers recently investigated the association between the CRV’s vertical position within the ONH and the sites of VF defects in glaucomatous eyes. In a previous study, they suggested that the CRV’s position changes with LC deformation, likely during the growth process of the eyeball, and hypothesized that glaucoma stress may be evaluated by using the CRV entry position into the LC instead of its exit position. More recent findings suggest that vertical retinal vessel (RV) position and VF defect site are related.
The researchers included 134 non-myopic glaucoma eyes and 61 controls in their study. Using enhanced depth imaging OCT, they identified the vertical position of the CRV at its exit point from the LC onto the ONH surface and its entry point into the LC from the retro-laminar ONH. They noted that the retro-laminar ONH region is not heavily affected by glaucomatous LC deformation and is therefore suitable as a stand-in for original RV position before glaucoma development.
“Eyes with CRV in the superior region of the ONH were significantly more likely to exhibit VF defects in the superior hemifields, and vice versa,” the researchers wrote in their paper. In 63% of eyes with superior VF defects, CRV entry position was in the superior ONH region. In 97.8% of eyes with inferior VF defects, CRV entry position was in the inferior ONH region. The team noted, “The vertical position of the CRV in the ONH wasn’t significantly different between glaucomatous and normal eyes both at entry and exit positions, suggesting that it was little altered by the development of glaucoma and remained close to the original position.”
“The present study suggests that the original position of the CRV in the ONH may influence regional variation in the susceptibility to glaucomatous stress,” they continued. They explained this was a result of varying distances between the CRV and Bruch’s membrane opening (BMO). “In eyes with CRV in the superior region of the ONH, the distance between the CRV and the inferior BMO is [greater] than that between the CRV and superior BMO,” they explained. “In this case, axons passing through the inferior ONH region are damaged, leading to superior VF defects. An opposite effect occurs in eyes with inferior VF defects.”
They also noted that the peripheral region of the ONH is reported to contain thinner LC beams and larger pores, making it more vulnerable to stress. “In eyes with an off-center CRV, the peripheral ONH region farther from the CRV may be less mechanically supported and more susceptible to glaucomatous stress and prone to be the initial site of axonal damage,” they wrote. “In addition, the vascular supply to the adjacent tissue may be better in the vicinity of the CRV than in the periphery.”
They concluded that there’s a significant correlation between vertical CRV position in the ONH and altitudinal VF defect sites. They proposed using the original position of the CRV to help predict initial VF defect sites.
Sawada Y, Araie M, Shibata H. Vertical position of the central retinal vessel in the optic disc and its association with the site of visual field defects in glaucoma. Am J Ophthalmol. May 25, 2021. [Epub ahead of print].